Natural slate tiles have long been used as a roof covering. Natural slate is a durable material and is considered to provide an aesthetically pleasing look or appearance to a roof. Natural slate tiles have an advantage as a roof covering in that they will not burn, and therefore they can be used in dry climates where the possibility of fires precludes wood shake roofs. Natural slate tiles are applied to a roof deck or roof framework one tile at a time in a labor intensive process, but the overall appearance of the roof of the individually laid tiles is deemed by the marketplace to be worth a premium price. One of the features of roofs of natural slate is that different sources of slate have different colors. Commonly available colors are gray or green, and different colors such as red are more scarce. Therefore, slate roofs typically have a predominant color, such as gray, with one or more additional accent colors interspersed to add variety. A typical mix of colors for a slate roof might include roughly 60 percent of the tiles having a light gray background color, about 15 percent of the tiles having a purple color, and about 25 percent of the tiles having a dark gray color.
As an alternative to the high installed cost of natural slate, roofing suppliers have developed plastic or polymer tiles, such as highly filled thermoset resin tiles. An example of such a polymer tile in the form of wood shake shingles is disclosed in U.S. Pat. Nos. 5,615,523 and 5,711,126, both to Wells et al.
One problem with applying tile roofs, such as natural slate roofs or polymer slate roofs, is that where two or more colors are used on the roof, care must be taken to assure that the tiles are not inadvertently laid down in such a manner that there are undesirable patterns or grouping of colors. A typical undesirable pattern is stair stepping or racking. It is considered unattractive to have repeat patterns of the accent colors, such as red or purple, that are interspersed with the background color, such as green. Also, areas of high concentration of the tiles of the accent colors are not desirable. Even when attempts are made to apply the tiles in an entirely random manner, patterning, either in the overall roof, or in localized areas, can be evident in the finished roof. Patterning is the existence of repeat patterns of various colors, or areas of high concentration of tiles of the accent colors, that are readily observable to the casual observer. In some cases concern for avoiding patterning, that might inadvertently result from having the installer apply the tiles in a traditional manner, have lead to the practice of having an architect or the installer draw up a plan for an entire roof, tile by tile. This greatly increases the installed cost of the roof, and reduces the number of installers qualified to apply such roofs.
Past attempts to provide an attractive, aesthetically pleasing roof appearance for tile roofs include the patterning method for laying shingles or tiles disclosed in U.S. Pat. No. 1,893,944 to Johnson. The system in the Johnson patent requires the use of hexagonal-shaped tiles that have a first color on one side and a second color on the other side. The tiles are invertable so that the installer can lay all of the tiles down on the surface and then flip over selected ones of the tiles to form the desired pattern. In order to facilitate installation, the Johnson patent states at page 3, line 19 that the installer can be supplied with a picture or photograph of the desired design to follow when laying out the pattern of the tiles or shingles. All of the patterns suggested involve diagonal bands of tiles of one color interspersed with diagonal bands of tiles of the other color. The system in the Johnson patent uses a numerical table to suggest numerous differences in selecting the tiles that are to be inverted, so that an indefinite number of designs--all symmetrical--can be produced. If the pattern is repeated by the installer, the pattern established at the beginning edge or side of the roof in the Johnson method will repeat itself across the roof. Alternatively if the installer chooses to vary the pattern according to the Johnson method, the roof will contain a continuously changing pattern that extends across the whole roof. In either instance, each of the patterns created by inverting some of the hexagonal tiles will be a symmetrical pattern. These patterns will be quite apparent to the casual observer observing the roof after its completion.
Another attempt to provide an attractive, aesthetically pleasing roof appearance for tile roofs is disclosed in a brochure by Weatherbest Corp entitle "Variegated Color Roofs of Weatherbest Stained Shingles". The Weatherbest brochure discloses that the different colored shingles are mixed together in the desired percentages of color mixing at the Weatherbest factory and then rebundled, thereby enabling the installer to lay the shingles just as they come from the bundle. While this method would enable the manufacturer to predetermine the exact proportion of the various colors, the overall pattern could not be predetermined since there would be no assurance that the installer would lay out the shingles according to the actual predetermined pattern. Furthermore, most roofing installers work by establishing themselves at a first position on a roof and then installing all the tiles in the entire reachable portion of the roof before moving to a subsequent position on the roof. Therefore, there would be resistance to applying the tiles one row at a time, across the entire width of the roof. An additional problem with the method of mixing tiles of different colors in the bundles before shipping is the expense of mixing and repackaging tiles of the different colors.
It would be advantageous if there could be developed a roof tile installation method that would impart an aesthetically pleasing appearance to the roof and would eliminate patterning. Such a method would ideally enable the roof tile installer to apply the tiles in a convenient and efficient manner, and would overcome other deficiencies of the previously known methods of tile installation.